If the public are more upset at someone calling someone else Scum, but not at the lies, then there we have a perfect example of the state of our country.
It's about language. 'Scum' is common, and not meant to be directed, 'upwards'. "We say that down to you, you mustn't say it up to us!"
More seriously, parliamentary privilege ought never to be needed. MPs should be able to make a point with facts and temperate lingo.